1962] 
Lindroth — Platypatrobus 
9 
the softwalled section of the dorsum. In side view it resembles a 
stalked button, but in dorsal view it is revealed as the side-face of 
a horizontal though somewhat elevated and irregular lamella with 
thickened margin. It seems to have no direct counterpart in any 
species of Patrobus or Diplous. 
In summary, the male genitalia of Platypatrobus provide no clue 
to its taxonomic relationship with its two closest relatives, Patrobus 
and Diplous. The intrageneric variation of the internal sac is so great 
in both genera that no single consistently separating detail could be 
discovered. And the male genitalia of Platypatrobus itself show little 
peculiarity. Possibly, the general simplicity of the internal sac, with 
complete lack of spine-like sclerites, could be regarded as a sign of 
primitive organization. But it should be remembered that the same 
applies to the depressus group of Diplous (Kuhnelt, 1941) as well 
as to Patrobus assimilis. 
The taxonomic position of genus Platypatrobus , therefore, has 
still to be judged on external characters. In these, the genus is clearly 
closer to Patrobus than to Diplous. This is shown by the protruding 
eyes and the strongly constricted neck, as well as by several structural 
details of the prothorax: the central furrow is deepened at base; the 
basal foveae are deep and well defined ; the front margin is strongly 
elevated (almost as in P. longicornis) , delimited basad by a deep 
transverse impression which is coarsely punctured (as in P. septen- 
trioms) and prolonged laterally to front-angles as an engraved line 
(as in P. longicornis , septentrionis, and foveocollis) . However, as in 
Diplous, there is no defined latero-basal carinula inside the hind angles. 
There are also good characters separating Patrobus and Diplous 
in the marginal region of the elytra 1 , not observed by earlier students 
(Darlington, 1938; Kuhnelt, 1941 ; Lindroth, 1961) : (1) the raised 
lateral bead is complete to apex in Patrobus, rather suddenly dis- 
appearing well before apex in Diplous 2 ; (2) the 9th stria is better 
developed in Diplous, still evident at the level of the meso-coxae, 
whereas in Patrobus it disappears anteriorly well behind this point; 
(3) the marginal row of setiferous punctures (on 9th interval) is 
almost continuous in Diplous, consisting of about 20 (19-24) punc- 
tures, whereas in Patrobus it is zb interrupted at middle and the 
number of punctures is reduced (8-14). Jeannel (1941, p. 565ft) 
Studied in the North American and (Patrobus) Scandinavian representa- 
tives of the two genera. 
This, however, is not quite constant in Diplous. An apparently undescribed 
species from the Kolyma River district, E. Siberia (V. N. Kurnakov). has 
the elytra margined to apex. 
